Method for differentiating vaginal secretory fluid or cervical mucus of pregnant woman suffering from threatened premature delivery

ABSTRACT

Described is a method for differentiating the vaginal secretory fluid or cervical mucus of a pregnant woman suffering from threatened premature delivery, which comprises measuring an amount of Interleukin-8 in the vaginal secretory fluid or cervical mucus. The above method makes it possible to differentiate the vaginal secretory fluid or the like of the pregnant woman suffering from threatened premature delivery with good sensitivity and therefore is useful for the detection, treatment or the like of premature delivery.

TECHNICAL FIELD

The present invention relates to a method for differentiating the vaginal secretory fluid or cervical mucus of a pregnant woman suffering from threatened premature delivery, which method is useful for the detection of premature delivery.

BACKGROUND ART

Premature delivery is one of the abnormalities which occur accompanied with pregnancy. It is caused by various reasons but ascendens infection, intrauterine infection and abruption of placenta are considered as main reasons.

In the case where the premature delivery occurs because of an infectious disease or chorionic amnionitis, the concentration of C-reactive protein (CRP) and the leukocyte count both in the blood of the mother's body show an increase so that premature delivery is checked by measuring these values.

It is however difficult to say that the CRP concentration and the leukocyte count are specific to the premature delivery, because they are the values available from the blood and show an increase even by the factors other than the premature delivery. In addition, the CRP is accompanied with the problem that it can be detected only in a trace amount in the blood so the sensitivity of the measurement is low. Thus, it is difficult to make diagnosis as premature delivery at early stages of pregnancy by measuring the CRP concentration or the leukocyte count in the blood.

On the contrary, a method of making diagnosis as abortion or premature delivery by measuring Interleukin-6 (IL-6) in the blood has recently been reported (Japanese Patent Application No. 209882/1993). This method however uses the blood from the mother's body as a specimen and therefore is not fully satisfactory from the viewpoints of inferiority both in sensitivity and specificity.

An object of the present invention is therefore to search a substance which will be an indication of premature delivery and to establish a method for differentiating it.

With the forgoing in view, the present inventors have conducted an extensive investigation. As a result, it has been found that an increase in Interleukin-8 (IL-8) in the vaginal secretory fluid or cervical mucus is specific to a pregnant woman suffering from the threatened premature delivery and the vaginal secretory fluid or cervical mucus of the pregnant woman suffering from the threatened premature delivery can be differentiated by measuring the IL-8 amount, leading to the completion of the invention.

DISCLOSURE OF THE INVENTION

The present invention relates to a method for differentiating the vaginal secretory fluid or cervical mucus of a pregnant woman suffering from threatened premature delivery, which comprises measuring an amount of Interleukin-8 in the vaginal secretory fluid or cervical mucus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a comparison in the IL-8 concentration in the vaginal secretory fluid between the normal pregnant women group (left) and the threatened premature delivery group (right).

FIG. 2 illustrates fluctuations in the IL-6 and IL-8 concentrations in the vaginal secretory fluid and the CRP concentration in the serum, each obtained from pregnant women who were diagnosed as threatened premature delivery, received treatment but lead to premature delivery.

FIG. 3 illustrates fluctuations in the IL-6 and IL-8 concentrations in the vaginal secretory fluid and the CRP concentration in the serum, each obtained from pregnant women who were diagnosed as threatened premature delivery but as a result of treatment, recovered and lead to full-term normal delivery.

BEST MODE FOR CARRYING OUT THE INVENTION

As the specimen usable in the present invention, either a vaginal secretory fluid or cervical mucus can be used. No particular limitation is imposed on the sampling method of it insofar as the sampling can be conducted without giving a damage to the vagina or the uterine cervix. Examples include the method in which sampling is conducted by attaching a tube such as silicone tube or a needle to the end of a syringe and then inserting it in the vagina; a method in which sampling is conducted by inserting the syringe itself into the vagina; a method in which an absorber, such as an applicator, is inserted into the posterior vaginal formix and then, is allowed to absorb therein cervical mucus. Of these, the method employing an applicator is convenient and is therefore preferred, with the use of a dacron applicator as the applicator being more preferred because it brings about an improvement in an extracting efficiency. When the specimen is sampled using the applicator, the impurities in the vagina are first removed by a tampon and then the sampling is conducted while ensuring the sampling by a colposcope.

The specimen so sampled can be provided as is for the measurement. It is however desired to use it after dilution or extraction, because the undiluted vaginal secretory fluid or cervical mucus has a markedly high viscosity and is often gelated or clotted. It is preferred to use a buffer having a pH of from 6 to 8 for dilution or extraction. Examples of the buffer include phosphate buffer, tris buffer and Good's buffer. It is more preferred that the pH of the buffer falls within a range of from 7.2 to 7.8.

With a view to conducting dilution or extraction of the specimen by using the above-exemplified buffer, when the specimen is sampled using, for example, a syringe, it is preferred to extract IL-8 of the specimen, which is in the gel or clotted form, in the buffer by crushing the specimen as if cutting it and mixing the crushed substance with the buffer. In this case, it is preferred to use the buffer in an amount of at least 5 times as much as that of the specimen to conduct sufficient extraction.

When the specimen is sampled using an applicator, it is preferred to extract the specimen in a buffer by dipping the applicator, which has absorbed therein the specimen, in the buffer and then stirring the buffer with this applicator.

Any known method can be used for the measurement of the IL-8 amount in the vaginal secretory fluid or cervical mucus insofar as it is a method which can measure the cytokine amount, for example, bioassay method or immunoassay method. It is particularly preferred to employ an immunoassay method.

For example, the IL-8 in the specimen may be measured by the ELISA method in a manner known per se in the art. For example, a 96-well microtiter plate sensitized with the first antibody, that is a monoclonal or polyclonal antibody specific to IL-8, is used as a solid phase and it is reacted with the specimen, whereby the antibody on the solid phase is combined with IL-8 in the specimen. The unreacted protein is removed by a washing operation, followed by the reaction with the second antibody, that is, an enzyme-labeled monoclonal or polyclonal antibody specific to IL-8, whereby a sandwich is formed by the antigen-antibody reaction via IL-8. After the excess second antibody is removed by washing, a solution of the substrate for the labeled enzyme of the second antibody is added for color development. The enzyme reaction is then terminated by a terminating solution. The absorbance is then measured by an absorptiometer, and the IL-8 concentration in the sample may be obtained by conversion from a calibration curve of a standard product.

Alternatively, a commercially-available sandwich ELISA kit for the measurement of IL-8 concentration can be used.

Based on the IL-8 amount measured in this way, the vaginal secretory fluid or cervical mucus of a pregnant woman suffering from the threatened premature delivery can be differentiated. Described specifically, the vaginal secretory fluid showing a value higher than the IL-8 amount of the normal pregnant woman is regarded as that of a pregnant woman suffering from the threatened premature delivery.

Thus, it is possible to differentiate the normal pregnant woman and the pregnant woman suffering from the threatened premature delivery by measuring the IL-8 amount in their vaginal secretory fluids or cervical mucus.

EXAMPLES

The present invention will hereinafter be described in detail by the following examples. It should however be borne in mind that the present invention is not limited to or by the examples.

Example 1

Concerning eight normal pregnant women who were different in each gestational age and eight pregnant women who had been diagnosed as threatened premature delivery, the IL-8 amount in the vaginal secretory fluid, the CRP concentration in the serum and the leukocyte count in the blood were measured as described below, respectively. These results are shown in Table 1, Table 2 and FIG. 1.

Sampling Method of Specimen

A dacron applicator was inserted in the posterior vaginal formix of each of the pregnant women. The applicator was turned round for about ten minutes to have the vaginal secretory fluid absorbed in it, followed by dipping in 1 μl of an extracting solution (which comprises 50 mM of 2-amino-2-hydroxymethyl-1,3-propanediol, 1% BSA, 0.89% of sodium chloride, 0.2% of disodium ethylenediaminetetraacetate, 1 μl/ml of aprotinin, 1 μl/ml of dimethylsulfoxide, 0.17 mg/ml of phenylmethylsulfonyl fluoride, 1 μl/ml of polyoxyethylenoctyl phenyl ether and 0.5 mg/ml of sodium azide; pH 7.5). The vaginal secretory fluid absorbed in the dacron applicator was extracted by stirring the extracting solution with the dacron applicator. The vaginal secretory fluid so extracted was used as a sample. Incidentally, the sample was used after dilution with the extracting solution as needed.

Measuring Method of IL-8

The IL-8 in the vaginal secretory fluid was measured, as will be described subsequently, in accordance with the measuring method of Quantikine of R & D. Described specifically, in each of the wells of the microtiter plate sensitized with a mouse anti-IL-8 monoclonal antibody, a 100 μl portion of an assay diluent was poured, followed by the addition of a 100 μl portion of the sample. The resulting mixture was then allowed to stand at room temperature for 2 hours to cause reaction, followed by washing of the well three times each with a 400 μl portion of a washing liquid. The washing liquid was thereafter removed. To each well, a 200 μl portion of a horseradish peroxidase-labeled (HRP) anti-IL-8 polyclonal antibody solution was added, which was allowed to stand at room temperature for 2 hours. After washing three times each with a 400 μl portion of the washing liquid, a 200 μl portion of a chromogenic solution containing tetramethyl bentidine as a substrate was added to each well, which was allowed to stand at room temperature for 20 minutes. To each well, a 50 μl portion of 2N sulfuric acid was added as a terminating solution, whereby the enzyme reaction was terminated. The wavelength of the microtiter plate reader was set at two wavelengths, that is, 450 nm and 550 nm, and an absorbance was measured. The IL-8 concentration in the sample was obtained from the calibration curve of the standard product by conversion.

The CRP concentration, on the other hand, was measured by a commercially available kit (product of IATRON LABORATORIES, INC., latex coagulation method) by using the serum of the pregnant woman as a sample. The leukocyte count was measured by an automatic blood cell counter of Sysmecks Corporation by using the blood of the pregnant woman.

                  TABLE 1                                                          ______________________________________                                         IL-8 Concentration in vaginal secretory                                          fluid of normal pregnant women group                                                                       IL-8                                               Patient No. Gestational age ng/ml                                            ______________________________________                                         1               6W        3.61                                                   2 14W 4.31                                                                     3 20W 2.52                                                                     4 21W 8.34                                                                     5 25W 1.50                                                                     6 27W 3.32                                                                     7 29W 2.67                                                                     8 35W 12.08                                                                  ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         IL-8 Concentration in vaginal secretory fluid, CRP concentration in serum       and leukocyte count in blood, of threatened premature delivery group                               In vaginal                                                                                        secretory liquid In serum In                                                blood                                       Patient Gestational IL-8 CRP Leukocyte count                                   No. age ng/ml mg/dl /mm.sup.3                                                ______________________________________                                         1      25W + 4d  292        0.30    9900                                         2 24W + 3d 128 0.00 10500                                                      3 32W + 3d 1680 16.40 12000                                                    4 25W + 2d 554 0.50  6800                                                      5 30W + 4d 890 0.30  7800                                                      6 28W + 2d 323 0.30 12700                                                      7 31W + 5d 41.5 0.00  5100                                                     8 26W + 1d 1430 2.80 16000                                                   ______________________________________                                    

The concentration of IL-8 in the vaginal secretory fluid was 1.5-12.1 ng/ml in the case of the normal pregnant women, while that was 41.5-1680 ng/ml in the case of the group of threatened premature delivery. According to the Mann-Whiteney's test, the IL-8 concentration of the latter group showed a significantly high value (p<0.001). From these results, it has been found that the measurement of the amount of IL-8 in the vaginal secretory fluid makes it possible to differentiate the vaginal secretory fluid of a pregnant woman who suffers from threatened premature delivery, thereby detecting the premature delivery.

On the contrary, there exist six samples, among eight samples of the threatened premature delivery group, which did not show an abnormal value in the CRP concentration (0.8 mg/dl or higher) in the serum so that premature delivery could not be detected effectively from the CRP concentration in the blood.

Concerning the leukocyte count in the blood, three examples, among eight examples of the threatened premature delivery group, showed a normal value (4,000-8,000/mm³) so that it was not impossible to detect all the threatened premature delivery cases from the test of the leukocyte count.

Example 2

FIG. 2 illustrates a case which was diagnosed as threatened premature delivery at the gestational age of 20 weeks, received a tocolysis treatment, but resulted in premature delivery on the fifth day after the treatment was started. The IL-6 and IL-8 concentrations in the vaginal secretory fluid and the CRP concentration in the serum are plotted along the ordinate, while the days after the first examination are plotted along the abscissa.

The IL-6 and IL-8 concentrations in the vaginal secretory fluid of a pregnant woman were measured by sampling and extracting the specimen in a similar manner to Example 1. The IL-6 and IL-8 concentrations were measured using an ELISA kit for IL-6 measurement (product of R&D) and an ELISA kit for IL-8 measurement (product of R&D), respectively.

Consequently, both the IL-6 and IL-8 concentrations continued increasing, resulting in the premature delivery. The IL-8 concentration is, however, by about 10³ higher than the IL-6 concentration so that the premature delivery can be detected with better sensitivity by using the IL-8 concentration. The CRP concentration in the serum, which had been used conventionally for the detection of the premature delivery, only showed an abnormal value just before the premature delivery.

Example 3

FIG. 3 illustrates a case which was diagnosed as the premature delivery at the gestational age of 30 weeks, received a tocolysis treatment and resulted in the full term delivery. The IL-6 and IL-8 concentrations in the vaginal secretory fluid and the CRP concentration in the serum are plotted along the ordinate, while the days after the first examination are plotted along the abscissa. The IL-6 and IL-8 concentrations in the vaginal secretory fluid of a pregnant woman were measured by sampling and extracting the specimen in a similar manner to Example 1.

The more stable the symptom became, the lowering tendency the IL-6 and IL-8 concentrations showed. For monitoring the judgment of the effects brought about by the treatment, the IL-8 concentration is superior because it is by about 10³ higher than the IL-6 concentration so that the premature delivery can be detected with better sensitivity by using the IL-8 concentration.

Example 4

Fluctuations in the IL-8 concentrations in the serum and in the vaginal secretory fluid of the threatened premature delivery group were measured in a similar manner to Example 1. The results are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         Comparison between IL-8 concentration in vaginal secretory                       fluid and that in serum, both of threatened premature delivery group                                In vaginal secretory liquid                                                                  In serum                                      IL-8 IL-8                                                                    Patient No. Gestational age ng/ml ng/ml                                      ______________________________________                                         1       27W + 3    154             <0.03                                         2 32W 73.80 <0.03                                                              3 33W + 1 737 <0.03                                                            4 37W + 1 89.50 <0.03                                                        ______________________________________                                    

The amount of IL-8 in the serum is as small as the lowest limit of the measuring range, while the IL-8 exists in the vaginal secretory fluid in an amount sufficient for the measurement. Accordingly, the use of the vaginal secretory fluid as a sample, said fluid being close to the object of the treatment, makes it possible to differentiate the vaginal secretory fluid of the pregnant woman suffering from threatened premature delivery even in a small amount and also to detect the premature delivery with better sensitivity than the use of the serum, plasma or blood.

Example 5

The IL-8, CRP in the serum and the leukocyte count in the blood were measured in a similar manner to Example 1 concerning the case which was diagnosed as threatened premature delivery at the gestational age of 30 weeks, received a tocolysis treatment but resulted in the premature delivery through caesarean section on the 20th day. The results are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         IL-6 and IL-8 Concentrations in vaginal secretory fluid (premature              delivery), CRP concentration in serum and leukocyte count in blood, of a       case beyond remedy                                                                           In vaginal                                                                                           secretory liquid In serum In blood                                            Days after first IL-8 CRP Leukocyte                                           count                                         examination ng/ml mg/dl /mm.sup.3                                            ______________________________________                                         The first exami-                                                                          890        0.3        7800                                            nation day                                                                     10th day 378 0.5 8500                                                          20th day 4120  3.7 14200                                                     ______________________________________                                    

From the results of the first examination day, it has been found that the IL-8 in the vaginal secretory fluid showed a high concentration which could be judged as abnormal, but the CRP concentration in the serum and the leukocyte in the blood each fell in its normal range. The IL-8 concentration continued to be high after that, leading to the premature delivery, while, the leukocyte count showed an abnormal value on the 10th day after the first examination and the CRP concentration became abnormal just before the premature delivery. Thus, the measurement of the IL-8 concentration in the vaginal secretory fluid makes it possible to differentiate the vaginal secretory fluid of a pregnant woman suffering from threatened premature delivery, and also to detect the premature delivery at earlier stages of the pregnancy compared with the measurement in the CRP concentration in the serum or the leukocyte count in the blood.

Example 6

Measured were the IL-6 and IL-8 amounts in the vaginal secretory fluid of 35 normal pregnant women who were different in each gestational age and 38 pregnant women who were diagnosed as threatened premature delivery. The sampling of the specimen and measurement of the IL-6 and IL-8 amounts were conducted in a similar manner to Example 1. The results are shown in Tables and 5 and 6.

                  TABLE 5                                                          ______________________________________                                         Group of normal  In vaginal                                                      pregnant women secretory fluid                                               Specimen             IL-6       IL-8                                             No. Gestational age ng/ml ng/ml                                              ______________________________________                                         1         6W         0.108      13.5                                             2  6W 0.807 8.0                                                                3  6W 0.132 3.6                                                                4 6W + 3d 1.475 14.4                                                           5 10W 0.277 43.1                                                               6 14W 0.000 4.3                                                                7 18W 0.188 10.4                                                               8 18W 0.142 104.2                                                              9 19W 0.339 4.3                                                                10 20W 0.000 2.5                                                               11 21W 0.130 44.2                                                              12 21W 0.077 41.2                                                              13 21W 0.000 8.3                                                               14 22W 0.177 44.3                                                              15 23W 0.111 59.8                                                              16 24W 0.106 84.6                                                              17 25W 0.000 1.5                                                               18 26W 0.138 59.3                                                              19 27W 0.162 3.3                                                               20 28W 0.082 50.9                                                              21 28W 0.076 22.9                                                              22 28W 0.295 42.4                                                              23 29W 0.000 2.7                                                               24 31W 0.000 44.6                                                              25 32W 0.000 26.9                                                              26 32W 0.130 87.0                                                              27 32W 0.121 21.5                                                              28 34W + 6d 0.237 19.8                                                         29 35W 0.096 12.1                                                              30 35W + 1d 1.667 50.9                                                         31 36W 0.134 40.6                                                              32 36W 0.090 41.8                                                              33 36W 0.211 68.7                                                              34 40W 0.227 12.3                                                              35 40W 0.888 23.5                                                            Average          0.246      32.10                                                Standard deviation 0.383 27.02                                                 Average + 2 standard deviation 1.012 86.14                                   ______________________________________                                    

                  TABLE 6                                                          ______________________________________                                                           In vaginal                                                     Group of threatened secretory fluid                                          premature delivery                                                                               IL-6   IL-8                                                    Specimen No. ng/ml ng/ml                                                     ______________________________________                                         1                 1.12   1,090                                                   2 3.95 467                                                                     3 3.36 888                                                                     4 0.95 292                                                                     5 1.61 128                                                                     6 0.00 410                                                                     7 0.10 82.3                                                                    8 0.22 227                                                                     9 4.98 180                                                                     10 0.14 332                                                                    11 0.00 108                                                                    12 0.81 808                                                                    13 0.33 101                                                                    14 0.00 96.7                                                                   15 0.21 98.5                                                                   16 0.08 423                                                                    17 0.23 137                                                                    18 0.00 535                                                                    19 1.91 1,120                                                                  20 1.23 316                                                                    21 0.70 282                                                                    22 1.56 295                                                                    23 1.35 43.6                                                                   24 3.07 449                                                                    25 0.32 2,440                                                                  26 1.14 625                                                                    27 0.34 126                                                                    28 10.60 204                                                                   29 1.77 1,190                                                                  30 5.73 1,680                                                                  31 7.83 554                                                                    32 0.42 890                                                                    33 0.74 323                                                                    34 1.61 42                                                                     35 13.00 1,430                                                                 36 2.89 1,064                                                                  37 0.39 110                                                                    38 0.00 144                                                                  ______________________________________                                    

The criterion on concentration (cut-off value) of threatened premature delivery was designated as the average value the IL-6 or IL-8 concentration in the vaginal secretory fluid in a normal pregnant woman+2 standard deviation, and the sensitivity and specificity of the IL-6 and IL-8 to threatened premature delivery were calculated in accordance with the following formulas, respectively. The results are shown in Table 7. ##EQU1##

                  TABLE 7                                                          ______________________________________                                                      IL-6    IL-8                                                      ______________________________________                                         Cut-off        1.012 ng/ml                                                                              86.14 ng/ml                                             concentration                                                                  Sensitivity 47% 92%                                                            Specificity 94% 94%                                                          ______________________________________                                    

As is apparent from the results in Table 7, compared with IL-8showed both high sensitivity and high specificity, which are the requirements for a detection reagent, so that it is useful for the detection of threatened premature delivery.

CAPABILITY OF EXPLOITATION IN INDUSTRY

According to the present invention, the vaginal secretory fluid or cervical mucus of the pregnant woman suffering from threatened premature delivery can be differentiated with better sensitivity, so that the method according to the present invention is useful for the detection, diagnosis and treatment of premature delivery. 

We claim:
 1. A method of diagnosing possible premature delivery comprising measuring a level of interleukin-8 (IL-8) in vaginal secretory fluid or cervical mucus of a pregnant woman suspected of premature delivery, comparing the level with that of a normal pregnant woman, and correlating an IL-8 level of 86.14 ng/ml or more in the pregnant woman suspected of premature delivery with a possibility of premature delivery.
 2. A method according to claim 1, wherein the vaginal secretory fluid or cervical mucus has been sampled by inserting a dacron applicator in the posterior vaginal formix, thereby having the vaginal secretory fluid or cervical mucus absorbed in it.
 3. A method according to claim 1, wherein the vaginal secretory fluid or cervical mucus which has been sampled is diluted or extracted with a buffer having a pH of from 6 to 8 prior to measurement of, the amount of Interleukin-8. 